Definition of successfulness in US English:

successfulness

noun

  • See successful

    • ‘Both employee and employer safety attitudes can determine the successfulness of a program.’
    • ‘To ensure the successfulness of landing operations the armed forces, and the US Navy in particular, began creating new units that could handle specific dangerous tasks that no one else could complete.’
    • ‘Interviewers also asked parents to rate the degree of suffering as a result of each symptom, whether the child received treatment for the symptom, and, if so, the successfulness of the treatment.’